1. Field
Compositions and apparatuses consistent with exemplary embodiments relate to photosensitive recording media, and more particularly, to holographic photopolymer compositions for recording a three-dimensional transmission and a reflective hologram, and hologram recording media.
2. Description of the Related Art
The development of novel photopolymer compositions for holographic recording has become nowadays a very important task in laser, optic, and polygraphic applications. In a photopolymer system for recording a hologram, a polymer product is formed from a monomer by laser exposure. As a result, an interference pattern is formed and the modulation of refractive index is generated to form a phase hologram capable of reaching high diffraction efficiency in the photopolymer system.
Disadvantages inherent in silver halide and dichromated gelatin commonly used for recording a hologram do not occur in the photopolymer material. That is, by using a photopolymer for holographic recording, multi-step post-treatments (including wet post-treatment) may be avoidable, and high quality holograms in may be recorded real time.
In contrast to silver halide materials, most known non silver halide photosensitive materials based on organic or inorganic compounds are not grainy and therefore can record data with high resolutions. However, disadvantages of the materials include a limited area having enough photosensitivity in a visible spectrum area. Thus, the enlargement of the photosensitive area is a priority task.
Single layered or multi-layered holographic photopolymer materials used for recording monochrome and polychrome holograms are known. U.S. Pat. No. 4,942,102 discloses a photopolymer composition for holographic photopolymer materials, including an acryl and/or vinyl-type monomer, a polymer binder (polyvinyl acetate, polyvinyl acetal, polyvinyl formal or polyvinyl butyral), a plasticizer, and a photoinitiation system. The photoinitiation system may include a photosensitizer such as a compound from bis(p-dialkylaminobenzylidene) ketone groups, an initiator such as 2,2′-bis(o-chlorophenyl)-4,4′,5,5′-tetraphenyl biimidazole, and a hydrogen donor such as 5-chloro-2-mercaptobenzothiazole, 2-mercaptobenzothiazole, 4-methyl-4H-1,2,4-triazole-3-thiol, or a mixture thereof.
The holographic materials based on the above-described composition may have a low diffraction efficiency (˜5%) in an image recording step, however, they may form a reflective hologram having a diffraction efficiency of about 70-80% after a heat treatment (at about 80-160° C.) and/or a wet treatment in an organic solvent. Besides, the heating of these materials at about 30-50° C. before performing an exposing process is recommended. Also, the wet treatment of these materials to increase the diffraction efficiency thereof may be additionally conducted, however, it is not essential.
The low diffraction efficiency of an image after exposure is one of the disadvantages of these materials. In some cases, for example, in order to obtain a series of transmission Fourier holograms, it is necessary to confirm the real time information quality. In order to accomplish this requirement, a diffraction efficiency of about 20-30% is necessary in a recording step.
Another photopolymer composition is disclosed in U.S. Pat. No. 4,959,284. This composition includes a cyclopropane compound as a monomer component, and also includes a well-known dye-sensitizer, 2,5-bis[4-(diethylamino)phenyl]methylene (DEAW). By using this composition, a hologram having a high diffraction efficiency, greater than or equal to about 90%, may be obtained in a blue spectrum area. However, the sensitivity of this composition is low: about 50-150 mJ/cm2.
U.S. Patent Publication No. 20100086860 discloses a photopolymer composition including unsaturated urethane derivatives having functionalized groups by monomer components. The amount of dissolved components in a polyurethane matrix is about 25 wt % based on the total amount of the composition. New methylene blue is used as a dye-sensitizer. By using the photoinitiation system, a monochrome hologram in only a red spectrum area may be recorded. This material has a sensitivity of about 5 mJ/cm2 and a diffraction efficiency of greater than or equal to about 70%.
U.S. Patent Publication No. 20110065827 discloses a photopolymer composition including another monomer component of unsaturated glycidyl ether acrylate urethane. A photo material capable of recording a hologram having a high diffraction efficiency (about 80%) was obtained by using the same dye, that is, the new methylene blue. The sensitivity was about 20 mJ/cm2.
U.S. Patent Publication No. 20120214089 discloses a method of preparing a photo material having sensitivity at wavelengths of 633 nm, 532 nm, and 437 nm. A photopolymer composition is based on a polyurethane matrix having an acrylate monomer and includes tetrabutylammonium tris(3-chloro-4-methylphenyl)hexylborate as a co-initiator. As a dye-sensitizer, new methylene blue (λmax=632 nm), safranine O (λmax=520 nm) and astrazone orange G (λmax=490 nm) are used. By using this composition, a hologram having a diffraction efficiency of about 99% was recorded. The sensitivity of this material was about 9-36 mJ/cm2 (λmax=633 nm), about 16-128 mJ/cm2 (λax=532 nm) and about 16-128 mJ/cm2 (λmax=473 nm). The dispersed values of the sensitivity are due to the low reproducibility of the experimental samples, and thus, limit the commercial application of the photopolymer materials.
In U.S. Patent Publication No. 20120086993, an acryloyl monomer component of 9,9-bis[4-(2-acryloyloxyethoxy)phenyl]fluorene) (Shin-Nakamura Chemical Co., Ltd., NK Ester A-BPEF) is used in a photopolymer composition. 3-Butyl-2-[3-(3-butyl-5-phenyl-1,3-benzoxazole-2(3H)-ylidene)propane-1-en-1-yl]-5-phenyl-1,3-benzoxazole-1-ium) is used as a photosensitizer in a blue-green area (λmax=510 nm), and 3-ethyl-2-[5(3-ethyl-1,3-benzoxazole-2(3H)-ylidene)penta-1,3-dien-1-yl]-1,3-benzoxazole-3-ium is used as a photosensitizer in a red-green area (λmax=595 nm). The thus obtained photopolymer materials in two layers may be used to record a hologram having a diffraction efficiency of about 80% and a sensitivity of about 6 mJ/cm2 at a wavelength of about 473 nm, a sensitivity of about 4 mJ/cm2 at a wavelength of 532 nm, and a sensitivity of about 40 mJ/cm2 at a wavelength of about 633 nm.
From the analysis regarding the dye spectrum, both dyes contribute to the sensitivity in the green spectrum area. An intersection sensitization due to a sensitizer having sensitivity to different colors may affect the recording of the hologram. For example, when a photosensitizer sensitizing in a blue-green area is used, the sensitivity of the photopolymer in a green area may be decreased by the decoloring of the photosensitizer due to the sensitization to a blue area light (the same applies to the reverse case). This feature must be considered when recording a full color hologram. The recording process of the full color hologram is more complicated because the sensitivity of the dyes in the full spectrum area is different.